Sewing machine v-belts and method for producing same



March 29, 1966 R. w. GRAFT 3,242,750

SEWING MACHINE v-BELTS AND METHOD FOR PRODUCING SAME Filed April 13, 1964 INVENTOR.

ROBERT W. GRAFT TTORNFY United States Patent 3,242,750 SEWING MACHINE V-BELTS AND METHOD FOR PRODUCING SAME l Robert W. Graft, Somerville, N.J., assignor to The Singer Company, New York, N.Y., a corporation of New Jersey Filed Apr. 13, 1964, Ser. No. 358,986 1 Claim. (Cl. 74234) This invention relates to a V-belt for sewing machines and the method for producing the same, and has as its principal object to provide an economical V-belt with a long life span.

The object of the invention is accomplished by preferably injection molding a V-belt in a single cavity mold using two gates 180 degrees apart at the outer circumference of the V-belt. Heated granules of a polyurethane compound such as the Mobay Chemical C-ompanys Texin No. 480-A are forced into the mold under pressure.

The resulting V-belt has an isosceles trapezoid shaped cross section, a plurality of isosceles triangular wedgeshaped teeth equally spaced around its inner circumference, a plurality of concave curvilinear depressions between the teeth blending into the faces of the teeth, and a solid outer circumferential band with a minimum radial thickness.

The polyurethane composition produces a belt with three times the life of the conventional cord reinforced rubber belts at approximately one half the cost. The slight elasticity of the new belt makes it easier to adjust the tension for variances in distance between centers of paired pulleys. The isosceles triangular wedge-shaped teeth around the inner circumference impart flexibility, the curvilinear depressions between the teeth prevent cracking, and the radial thickness of the outer circumferential band provides adequate frictional contact with the pulleys.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claim, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a standard and elevational view of a sewing machine having the belt of the present invention employed to connect an exteriorly mounted motor with its driving pulley,

FIG. 2 is a detail elevational view of the pulleys shown in FIG. 1,

FIG. 3 is a perspective view of the V-belt.

FIG. 4 is a detail side elevational view of an arc of the V-belt, and

FIG. 5 is a cross sectional view taken along the line 55 of FIG. 4.

With reference to the drawings, the invention is illustrated as embodied in a conventional sewing machine having an electric motor mounted on the outside of the sewing machine standard 11. The sewing machine is equipped with the usual handwheel 12 connected to the end of a main shaft 13. The motor has a rotor shaft 14 positioned parallel to the main shaft of the sewing machine.

A V-belt 20 is looped tautly around a pulley 21 formed in the handwheel 12 of the sewing machine and a smaller pulley 22 mounted on the rotor shaft 14 of the motor 10. V-shaped grooves 23 and 24 are formed respectively in the circumferences of the pulleys 21 and 22 with sides flaring outwardly preferably at 20 degree angles to accommodate the V-belt.

3,242,750 Patented Mar. 29, 1966 The V-belt 20 is composed of a homogeneous polyurethane compound such as the Mobay Chemical Companys Texin No. 480A, heated granules of which have been forced into a single cavity mold under pressure through two gates degrees apart at the outer circumference of the V-belt. The slight elasticity of polyurethane makes it easier to adjust the tension of the belt for variances of distance between the centers of paired pulleys. The use of only two gates at the outer circumference of the belt reduces the incidence of failure at the Welds produced by the gates. While the above described method represents a successful way of producing the present belt, the belts could also be produced by machining cast sleeves having an internal bore formed with teeth.

In a preferred embodiment of the invention, the belt 20 has an inner circular radius 30 and an outer circular radius 31 with teeth 32 equally spaced around the inner circumference of the belt thereby to impart suflicient flexibility to the belt. Each tooth 32 has an isosceles triangular wedge-shape with the equal faces meeting at a dihedral angle of from 36 to 44 degrees at the apex 33. Circular depressions 34 are formed between the teeth and blend into the opposed equal faces of adjacent teeth. The circular depressions prevent cracking between the teeth.

The transverse cross-section of the V-belt 20 is an isosceles trapezoid with its equal nonparallel sides flaring outwardly at substantially 20 degree angles to match the contours of the V-shaped grooves 23 and 24 in the pulleys 21 and 22. Tests have shown that to prevent slippage a minimum radial thickness of 0.05 of an inch for the solid outer circumferential band of the V-belt is necessary to achieve adequate frictional contact with the pulleys. It is within the scope of the invention to make the grooves of the pulleys out of a different material to increase the frictional characteristics of the pulleys. However, one of the inherent advantages of the present invention is that the molded polyurethane belts are directly interchangeable with the cord reinforced rubber belts now being used on many models of present day sewing machines.

What is claimed is:

A toothed V-belt for a pair of pulleys on a sewing machine, said toothed V-belt having a molded homogeneous polyurethane composition, a solid circumferential band with a minimum radial thickness of at least 0.05 of an inch, and a plurality of substantially triangular wedgeshaped teeth having equal faces forming dihedral angles at their apexes of from 36 to 44 degrees and equally spaced around and integral with the inner circumference of said outer circumferential band with concave curvilinear depressions formed between the teeth which are blended into the faces of the teeth.

References Cited by the Examiner UNITED STATES PATENTS 585,416 6/1897 Wattles. 1,828,136 10/1931 Freedlander 74229 2,540,245 2/1951 Dean 74234 2,662,497 12/ 1953 Johnson 112218 2,805,182 9/ 1957 Hallenbeck 74231 2,988,029 6/ 1961 Herbst 112-220 3,016,756 l/1962 Jackel 74234 DAVID J. WILLIAMOWSKY, Primary Examiner. DON A. WAITE, Examiner.

J. A. WONG, Assistant Examiner. 

